34 Loe AUD UB ONS Bir ele ieee 
Cornell Biologist Offers Fresh Evidence 
In Debate Over DDT vs. Birds of Prey 
RECENT FINDINGS by a Cornell University researcher may put an end to 
a longstanding argument over certain harmful effects of DDT—a persistent 
insecticide which has been officially banned in the United States. 
David B. Peakall, senior research associate in the Section of Ecology 
and Systematics in Cornell’s Division of Biological Sciences, said that al- 
though DDT has been blamed by many authorities for the demise of the 
Peregrine falcon, the issue remains hotly debated in public and private. 
DURING THE 1960s naturalists noted that populations of Peregrines 
had decreased drastically in Europe and North America. In 1967 Derek 
Ratcliffe of the Nature Conservancy in England discovered a basic cause 
of this demise: the Peregrine eggshells had become so thin that they often 
broke before the young could hatch. Looking at museum specimens of col- 
lected eggs, scientists could track these thinner shells all the way back to 
1947, when DDT was introduced. 
“Opponents of the pesticide were sure that the chemical was to blame,” 
Peakall said, “since the birds of prey feed on the animals and birds who 
eat the insects which have been contaminated with it. 
Proponents, however, said that the eggshell thinning phenomenon 
followed the introduction of DDT too closely to be caused by it. 
THE LACK OF definitive evidence kept the argument going, Peakall 
said. Recently, Peakall devised a method for extracting from the membrane 
of the eggshell one of the metabolities of DDT—a form the chemical takes 
after it has been partially broken down by the mother’s body. 
Since the technique does not destroy the delicate shells, Peakall was 
able to borrow some Peregrine eggshells gathered in the late 1940s from 
the Western Foundation of Vertebrate Zoology. Testing these eggs, Peakall 
found that the DDT metabolite was present in sufficient amounts to have 
caused the thinning of the shells. 
“BEING AT THE TOP of their food chain,” Peakall explained, ‘‘preda- 
tory birds ingest the greatest doses of insecticides. Since the initial intro- 
duction of DDT was in relatively small quantities, some scientists felt that 
too many coincidences would have had to occur for DDT to be responsible 
for the thinning of the shells. This new evidence should change that idea.” 
Peakall’s work is supported by the National Institute of Environmental 
Health Sciences, one of the National Institutes of Health (NIH), a part of 
the U.S. Department of Health, Education and Welfare (HEW). 
ALTHOUGH AN ARGUMENT may have been settled and the pesticide 
banned, Peakall’s work continues in order to discover the mechanism that 
causes the thinning, the dose required and the nature of the enzyme changes 
in the oviduct of the mother bird. Peakall is using Kestrels, another 
predatory bird, as the test subjects in this study. 
Another aspect of his research is an adjunct to the Peregrine breeding | 
program at Cornell under Tom J. Cade, professor of zoology and research | 
